1. Field of the Invention
The present invention relates to a liquid crystal display device attached to the cover body of a laptop computer, a notebook type personal computer or the like to display images and a portable information terminal device having such a device.
2. Description of the Related Art
A portable information terminal device such as a laptop computer is provided with a keyboard at the top of the main body. The cover body to be lifted up and down and cover the keyboard is pivotally supported along the upper edge of the main body. The cover body is provided with a liquid crystal display device to display images.
The liquid crystal display device has an integral structure having a liquid crystal display panel (hereinafter as the xe2x80x9cLCD panelxe2x80x9d) held between a backlight unit and a picture frame-like presser casing. In the backlight unit, a plurality of diffusion sheets, a plurality of prism sheets, an optical guide plate and a reflector sheet are sequentially placed upon one another. At the lower part of the optical guide plate, a light source lamp and a reflector mirror (reflector) are provided. These are secured to a plate-like frame body (hereinafter as xe2x80x9cchassisxe2x80x9d) serving as a base.
The optical guide plate serves to propagate light emitted from the light source lamp upward and evenly supply the light over the entire display surface of the LCD panel. The optical guide plate has a rectangular shape when viewed two-dimensionally and a wedge-shaped cross section, for example. More specifically, the lower edge side closer to the light source lamp is thicker and the upper edge side farther from the light source lamp is thinner.
FIGS. 1A and 1B are schematic views showing how the optical guide plate is: secured to the chassis. On both side edges of the optical guide plate 101, there is a projection 102 projecting outward. Meanwhile, at a height in alignment with the projection 102 on the side frame of a chassis 100, a recessed portion 103 is formed. The engagement of the projection 102 with the recessed portion 103 secures the optical guide plate 101 at a prescribed position of the chassis 100.
Thus, even if for example the portable information terminal device having the liquid crystal display device is dropped, and large impact is applied upon the liquid crystal display device, the light source lamp can be prevented from being damaged as a result of the optical guide plate 101 moving downward to press the light source lamp (not shown).
It should be noted that the liquid crystal display device shown in FIG. 1B has a broader display surface than that shown in FIG. 1A, and an inner side 105 of the frame is positioned closer to the edge portion of the optical guide plate 101 in FIG. 1B than that shown in FIG. 1A.
The portable information terminal devices have been reduced in size to cope with the demand in the market, and the model whose main body is almost as small as the size of the keyboard has been recently marketed. There has also been a demand for a device with an enlarged display surface as well while there has been the demand for reducing the size of the main body. In order to satisfy these demands in the market, the frame portion of the cover body tends to be narrowed in recent portable information terminal devices.
For example, in a laptop computer, the cover body has an outer size almost the same as the main body. Therefore, if the size of the main body is further reduced, the cover body is reduced in size accordingly. When the display surface is to be expanded in the cover body whose size is to be further reduced, only the display surface is expanded with the width of the frame being narrowed.
It is generally known that in a conventional liquid crystal display device, as shown in FIGS. 1A and 1B, a luminescent spot 106 (hatched) is generated at a position in close proximity to the upper part of the projection 102. This is caused because the projections 102 are provided at both side edges of the optical guide plate 101 through which light must be homogeneously propagated at any positions. More specifically, the reflection state of the light changes by the presence of the projections 102, and the homogeneity of propagation is lost, which causes light and dark areas to be generated at the position in the close proximity of the upper part to the projections 102.
The luminescent spot 106 is hidden by the frame 105 of the cover body if the frame 105 has a relatively large width as shown in FIG. 1A. Therefore, the spot does not appear in the actual display surface and it was not a significant problem before the attempt to reduce the width of the frame 105 as described above. However, as the width of the frame has come to be narrowed as described above, as shown in FIG. 1B, the luminescent spot 106 appears on the display surface. Therefore, an image near the frame is difficult to view.
It will be described how such a fixed structure as shown in FIGS. 1A and 1B have come to be employed in the conventional device.
As stated above, it would be readily conceived to provide projections on the side edge of the optical guide plate and recesses on the chassis and let them engage with each other in order to prevent the light source lamp from being damaged by the optical guide plate. However the positions where the projections and recesses are provided are not arbitrary. More specifically, the presence of the luminescent spot itself is a problem to be addressed even if it could be covered by the frame. Therefore, the possibility of providing them at the upper or lower part of the side edges believed to be less susceptible to the influence of the luminescent spot was originally considered, but the idea was turned down for the following reasons.
The optical guide plate lets light emitted from the light source lamp upward and supplies light homogeneously over the entire display surface as described above. The optical guide plate can carry out the function successfully if it has a wedge-like cross section with a thicker lower edge side and a thinner upper edge side. Therefore, in order to reduce the weight of the liquid crystal display device as much as possible, the wedge shape as described above is employed for the optical guide plate. If a projection is provided on an upper portion of a side edge of the optical guide plate having the wedge shape, however, impact applied thereupon by falling could cause a crack at the base of the projection because the thickness at the part of the optical guide plate is small. This is a reason for turning down the idea of providing a projection at the upper part (the first reason).
The amount of light propagated through the optical guide plate increases toward the lower edge (closer to the light source lamp) and decreases toward the upper edge (farther from the light source lamp). This is because the light scatters from the display surface as it propagates. Therefore, if a projection is provided at a lower portion of the side edge of the optical guide plate, the amount of light is greater at the portion with the projection and greater difference results between the dark and light areas in the closer proximity with the projection. As a result, the luminescent spot becomes clearly visible. This is a reason for turning down the idea of providing the projection at the lower part (the second reason).
In view of the first reason, the projection is preferably provided at a position closer to the lower edge (thicker side). Meanwhile, in view of the second reason, the projection is preferably provided at a position closer to the upper edge (farther from the light source lamp). As a result, the fixed structure having the projection at the center of the side edge as shown in FIGS. 1A and 1B has been employed as a compromise between the first and second reasons. In this structure, the luminescent spots appear in the middle stages on both sides of the display surface, but they were not such a significant problem when there was not much need for reducing the width of the frame because these luminescent spots were covered and hidden by the frame.
Furthermore, the optical guide plate is generally manufactured by resin molding. In order to provide a wedge-shaped cross section, a mold into which resin is injected from the lower edge side (thicker side) to the upper edge side (thinner side) is used. However, when the projection is provided at the upper part of the side edge, the recessed portion to define the shape of the projection is apart from the resin inlet, and therefore the resin is less likely to reach to the position. This could cause additional processing work or processing precision may be lowered.
For example, Japanese Patent Laid-Open Publication No. Hei. 10-48427 discloses a surface light source device provided with securing means at a position corresponding to the upper edge (thinner side) of the optical guide plate. In the conventional surface light source device, there is a stopper like a turned part along the tip end (upper edge) of an optical guide plate. The stopper is engaged with a recessed portion provided at a frame to secure the optical guide plate to the frame. It should be noted that the frame corresponds to the presser frame or the chassis.
In the surface light source device disclosed in the publication, the stopper is provided at the entire tip end of the optical guide plate, and therefore force acting upon the optical guide plate is dispersed. As a result, there would be no problem in terms of strength against impact at the time of falling for example. However, it should be extremely difficult to form a stopper in such a complicated form at the tip end of the optical guide plate which is probably manufactured by molding as described above.
For example, Japanese Patent Laid-Open Publication No. Hei. 9-243828 discloses a surface light source device provided with securing means at a position corresponding to the lower part of the side edge of the optical guide plate. The conventional surface light source device has a raised portion for positioning integrally formed on a side surface of a light incident surface side (at the lower portion of the side edge, on the thickest part side). The raised portion is supported by a recessed portion of a frame to secure the optical guide plate to the frame.
In the surface light source device disclosed in the publication, the raised portion has a complicated polygonal shape, and luminance variation is alleviated by reflecting incident light to the raised portion upon each surface. However, also in this case, it would be extremely difficult to form such a raised portion in a complicated shape as shown in the publication at the optical guide plate which is probably manufactured by molding as described above.
This is how the optical guide plate has come to be secured in the above manner. This structure however allows the luminescent spot to be visible on the display surface, as the demand to narrow the frame has to be satisfied. Therefore, there is a demand for a structure which can prevent the effect of the luminescent spot while the frame is attempted to be narrowed.
It is an object of the present invention to provide a liquid crystal display device and a portable information terminal device capable of making less visible a luminescent spot which causes a problem in narrowing the frame of the cover body, and clearly displaying images in the vicinity of the frame.
According to one aspect of the present invention, a liquid crystal display device comprises a light source lamp, an optical guide plate which guides light emitted from the light source lamp, a liquid crystal display panel provided on the optical guide plate and a frame body to integrate the light source lamp, the optical guide plate and the liquid crystal display panel. The optical guide plate includes, a rectangular plate-shaped base portion, a rectangular plate-shaped projection which projects from an edge of said base portion, and a width expanded portion provided at a corner portion between said base portion and a farther side surface of said projection viewed from the side of said light source lamp. The projection projects in the direction perpendicular to the advancing direction of said light in said base portion and parallel to the plate surface of said base portion. The Width of said width expanded portion progressively increases toward said optical lamp. The frame body has a recessed portion to which said projection and said width expanded portion engage.
According to the aspect of the present invention, when light propagating through the inside of the optical guide plate is incident on. the width expanded portion, the light is reflected upon the boundary of the width expanded portion and diffuses, so that the difference between the dark and light areas is reduced. As a result, a luminescent spot in the vicinity of the projection and seen from the display surface becomes less visible.
In addition, the width expanded portion allows the projection to be less susceptible to damage by impact caused in falling or the like. In the conventional optical guide plate, there is a corner portion of 90xc2x0 at the root of the projection, in other words between the projection and the side edge, thereby a crack might be generated by stress concentration at the corner portion caused by impact applied upon the optical guide plate. In contrast, according to the present invention, impact upon the optical guide plate will not cause stress concentration between the projection and the edge of the base portion. Therefore, the impact resistance and oscillation resistance of the liquid crystal display device are improved.
Furthermore, the width expanded portion allows the productivity of the optical guide plate to be improved. As described above, an optical guide plate is manufactured by resin molding, and at the time of injecting resin into a mold typically, the resin coming into the recessed portion to define the projection flows along the edge of the width expanded portion. Therefore, the fluidity of the resin improves, which facilitates the injection operation. In addition, the improved fluidity reduces the residual stress generated in the projection molded by the recess. Therefore, the optical guide plate can be prevented from being deformed by the residual stress after curing, and the workability are improved.
If a portion perpendicular to the edge of the base portion from which the projection projects is provided at the further side surface, the direction of force acting upon the region between the projection and the recessed portion through the portion is substantially parallel to the edge of the base portion. As a result, when impact is applied, the force restricting the vertical movement of the optical guide plate acts in the direction opposing the moving direction of the optical guide plate. Therefore, a luminescent spot or a luminescent line can be prevented from being generated in association with a shift of the optical guide plate on the frame body.
When the width expanded portion has an edge of a smooth curved surface shape, light being incident on the width expanded portion is reflected upon and is diffused in a wider range. Therefore, the difference between dark and light areas is further reduced, so that the luminescent spot is less visible. At this time, a portion perpendicular to the edge of the base portion is. necessarily present between an end portion of the width expanded portion and the further side surface of the projection if the radius of curvature of the edge of the curved surface shape is not more than the projecting width of the projection. Thus, the force restricting the vertical movement of the optical guide plate acts upon in the direction opposing the moving direction of the optical guide plate through the portion as described above. Consequently, a luminescent spot or a luminescent line can be prevented from being generated in association with a shift of the optical guide plate on the frame body.
Similarly, if the width expanded portion has an edge including a plurality of planes, preferably a polygonal shaped edge resembling a smooth curved surface, light being incident on the width expanded portion is reflected and diffused in a wider range. This reduces the difference between dark and light areas, and the luminescent spot becomes less visible.
When the width expanded portion has an edge of a shape formed by combining a smooth curved surface and a plurality of planes or a plane edge, the reflecting direction of the light can be adjusted. As a result, the difference between dark and light areas can be arbitrarily reduced.
According to another aspect of the present invention, a liquid crystal display device comprises two light source lamps, an optical guide plate provided between the two light source lamps which guides light emitted from the light source lamps, a liquid crystal display panel provided on the optical guide plate and a frame body which integrates the light source lamps, the optical guide plate and the liquid crystal display panel. The optical guide plate comprises a rectangular plate-shaped base portion, a rectangular plate-shaped projection which projects from an edge of said base portion, and width expanded portions provided at corner portions between each side surface of said projection and. said base portion. The projection projects in the direction perpendicular to the advancing direction of said light in said base portion and parallel to the plate surface of said base portion. The width of said width expanded portions progressively increases toward said optical lamp provided at the opposite side in respect of said projection. The frame body has a recessed portion to which said projection and said width expanded portions engage.
Also in this case, the light propagating in the optical guide plate is reflected and diffused at the boundary of the width expanded portion. Therefore, the difference between dark and light areas is reduced at a position in the vicinity of end surfaces above and under the projection, so that the luminescent spot becomes less visible. Furthermore, similarly to the above described liquid crystal display device, the strength of the projection against impact caused by falling or the like is improved and the productivity of the optical guide plate improves as well.
According to another aspect of the present invention, a portable information terminal device integrates any of the liquid crystal display devices described above. Therefore, a luminescent spot on the screen is less visible, and the display surface is more acceptable. The impact resistance and oscillation resistance are improved and the device becomes easier to handle. In addition, the productivity of the optical guide plate is improved, which reduces the manufacturing cost.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.